1. Technical Field
The present invention relates to a light regulation device for regulating the travelling direction of light. and more particularly to a light regulation element for regulating the travelling direction of the light emitted from a surface light source device.
2. Description of Related Art
Where a surface light source device is applied to the backlight of a liquid crystal display, a range in which the display contents of the liquid crystal display can be clearly and visually recognized, that is, a view angle, and a brightness observed when the display screen is watched are affected by the travelling direction and spread of the light emitted from the surface light source device.
The more diffused the light emitted from the surface light source device, the wider the view angle becomes, but the darker the display becomes.
On the contrary, the less diffused the emitted light, the narrower the range of view angle becomes, but the larger the quantity of the light travelling in a specific direction becomes. When the display is watched in a direction corresponding to the light travelling direction, the display is observed to be bright.
On the contrary, when the direction in which the display is watched is largely deviated from the light travelling direction, the contrast of the display is lowered to cause the display contents not to be visually recognized.
Thus, where a surface light source device is applied to the backlight of a liquid crystal display, it has been necessary to change the diffusion state and travelling direction of the light emitted from the surface light source device in such a manner that the view angle and the display required for the liquid crystal display are adapted to the watching direction.
Also, where a surface light source device is used for a local illumination for illuminating a specific area, the more diffused the light, the wider area the device can illuminate, but the lower the illuminance becomes. On the contrary, the less diffused the light, the narrow area the device illuminates, but the higher the illuminance becomes.
Of course, also for the local illumination, the regulation of the light travelling direction is important, so that the light is required not to proceed in an undesirable direction.
According a conventional a method of changing the diffusion state and travelling direction of the light emitted from a surface light source device, both a diffusion element are arranged and a light regulation element are arranged on the emission surface of a surface light source device.
FIG. 5 illustrates an example of the configuration of a conventional surface light source device. Referring to FIG. 5, a cylindrical light source 2 is arranged along an incident surface 1b of a light guide 1. Arranged on an emission surface 1a of the light guide 1 are a light regulation element 3 and a diffusion element 6 in a state in which they are overlapped in a manner not to completely contact to each other. Arranged on the surface on the side opposite to the emission surface 1a of the light guide 1 is a reflection element 4.
The light emitted from the light source 2 enters the light guide 1 from the incident surface 1b of the light guide, and part of the light while travelling in the light guide 1 is emitted directly from the emission surface 1a. And another part of the light is reflected by a rough surface (not shown), or an ink print portion or the like formed on the light guide 1, and emitted form the emission surface 1a.
The light emitted from the emission surface 1a penetrates the light regulation element 3. The light travelling direction is bent by the action of many protrusions 3a provided on one surface of the light regulation element 3, whereby the light travelling direction is regulated in a desirable direction. Then, the light penetrates both a very narrow gap 10 (shown exaggeratedly in FIG. 5 ) formed between the light regulation element 3 and the diffusion element 6 and then the diffusion element 6, whereby the diffusion state of the light can be changed to a desired one.
However, for the surface light source device shown in FIG. 5, it is necessary to arrange both the light regulation element 3 and the diffusion element 6 on the emission surface 1a of the light guide.
If foreign matters such as dirt and dust adhere onto optical parts, or a flaw occurs thereon, the performance thereof will be remarkably deteriorated. Particularly for a surface light source device as shown in FIG. 5, there has frequently occurred a problem in that foreign matters are caught between the light regulation element 3 and the diffusion element 6 in the manufacturing process thereof.
Also where the surface light source device is assembled, individual parts must be checked to make sure there is no flaw or dirt, and then assembled with meticulous care. As a result, an increase by only one in the number of parts causes the manufacturing cost to be significantly increased.
Further, means for fixing both the light regulation element 3 and the diffusion element 6 are necessary, so that the size of the surface light source device tends to be large.
Further, a fact that the gap 10 consisting of an air layer exists between the light regulation element 3 and the diffusion element 6 generally means that, a layer having a refractive index much smaller relatively exists between the light regulation element 3 and the diffusion element 6. Therefore, although the gap 10 has an effect of diffusing the light, the gap 10 also causes the light utilization efficiency to be decreased due to the reflection on the interface with both the elements 3 and 6.